This invention relates generally to semiconductor devices that employ corrosive metal, such as copper, and more particularly to the corrosion that results when using corrosive metal such as copper in semiconductor devices.
Since the invention of the integrated circuit (IC), semiconductor chip features have become exponentially smaller and the number of transistors per device exponentially larger. Advanced IC""s with hundreds of millions of transistors at feature sizes of 0.25 micron, 0.18 micron, and less are becoming routine. Improvement in overlay tolerances in photolithography, and the introduction of new light sources with progressively shorter wavelengths, have allowed optical steppers to significantly reduce the resolution limit for semiconductor fabrication far beyond one micron. To continue to make chip features smaller, and increase the transistor density of semiconductor devices, IC""s have begun to be manufactured that have features smaller than the lithographic wavelength.
Semiconductor devices have traditionally been externally and internally wired by aluminum. The semiconductor industry has used aluminum wiring on chips for over thirty years. But the ever-shrinking universe of semiconductors has made aluminum more and more problematic, since it resists the flow of electricity as wires are made ever thinner and narrower. Therefore, semiconductor designers have tried to use alternative metals to aluminum. One such metal is copper. Copper is a superior conductor of electricity, making it possible to shrink the electronic devices even further while further increasing performance. But copper poses problems.
One such problem is corrosion. Corrosion of semiconductor device copper connections and interconnects can cause chip failure. Corrosion can increase the resistance of these connections and interconnections, nullifying copper""s inherent lower resistance and thus one of the advantages of using copper in semiconductors. Furthermore, corrosion can cause a semiconductor device to malfunction. The copper contacts may corrode together, causing shorts. Corrosion can also cause rapid thickness loss of the copper being corroded. Copper corrosion occurs especially during chemical-mechanical polishing (CMP). This is particularly problematic, because CMP is used to expose metal contacts for subsequent connecting. Where the metal contacts are copper, this means that corrosion and its deleterious effects may occur during CMP.
FIGS. 1 and 2 show an example of the corrosion process with respect to an illustrative connection of a semiconductor device 100. FIG. 1 shows a cross-sectional side view of the device 100, whereas FIG. 2 shows a top view of the device 100. An insulating layer 102, which can be fluorinated silicate glass (FSG) , is impregnated with a line of copper 104, which rises up to form a via, a pad, or a contact 108. As a result of time, or certain semiconductor fabrication processes such as CMP, electrons, as represented by the arrows 106, migrate towards the contact 108. This results in the corrosion 110, because current flows from the line of copper 104 to the contact 108.
The copper corrosion problem is especially severe where, such as in the device 100, there is only a small effective anode, such as the single contact 108, at which corrosion occurs. This is because the corrosion current is concentrated onto a small anodic area. The corrosion current emanates from the line of copper 104, which acts as a cathode in this process. The relatively large cathodic area of the line of copper 104 versus the relatively small anodic area of the contact 108 intensifies the corrosion 110. That is, a large amount of current emanates from the line of copper 104, owing to its large size, but this large amount of current congregates to a relatively small anodic area of the contact 108, causing substantial corrosion of the contact 108.
Therefore, there is a need for employing copper in semiconductor devices that overcomes these disadvantages. More specifically, there is a need for employing copper in a way that prevents corrosion and/or its deleterious effects. There is a need for preventing corrosion and/or its deleterious effects especially where there is only a small effective anodic area, such as where there is only a small number of contacts. For these and other reasons, there is a need for the present invention.
The invention relates to reducing metal corrosion, such as copper corrosion, in semiconductor devices. A semiconductor device includes an insulating layer, a metal line, one or more corrosive metal components, and one or more sacrificial corrosive metal components. The metal line is situated within the insulating layer. The one or more corrosive metal components are situated within the insulating layer and connected to the metal line. The one or more sacrificial corrosive metal components are situated within the insulating layer and connected to the metal line. The presence of the sacrificial components substantially reduces corrosion of the non-sacrificial components.
Embodiments of the invention provide for advantages over the prior art. The metal line acts as a cathode, whereas the corrosive metal components and the sacrificial metal components act as anodes. Corrosive current therefore flows from the cathode to the anodes. However, the sacrificial metal components substantially absorb the corrosive current emanating from the metal line. This substantially reduces, if not eliminates, corrosion of the non-sacrificial metal components. Still other advantages, aspects, and embodiments of the invention will become apparent by reading the detailed description that follows, and by referring to the accompanying drawings.